Modulating apparatus



Patented Aug..18, 1942 UETED TTS -MODULATING APPARATUS ApplicationNovemher 36, 1940, Serial No. 365,913

(61. lid) ll Claims.

This invention relates to a signaling transmis sion system, and'moreparticularly to a modulating arrangement to introduce into such systemcounter-distortion to compensate for the distortion generated by thecomponents of the system such as one or more repeaters arranged intandem.

in the copending application of E. Peterson, Serial No. 257,047, filedFebruary 18, 1939, now Patent No. 2,233,061, issued February 25, 1941,an arrangement utilizing a non-1inear resistance apparatus introducesinto a repeater transmission system third order modulation products inphase opposition to third order modulation products generated by therepeaters so as to efiect neutralization of the latter products. Inorder to obtain substantially maximum neutralization by sucharrangement, it is necessary that the non-linear apparatus and repeatersfollow substantially thesame law of variation of the modulation productsin response to varying amplitudes of applied signaling voltage.Accordingly, this invention contemplates a self-biasing modulatingapparatus that follows a certain law of variation of the modulationproducts over a range of sig-- naling voltage amplitudes.

It is a main object of the invention to control the law of variation ofa non-linear apparatus embodied in a modulating system.

It is a further object to apply a varying selfbiasing voltageto anon-linear resistance apparatus in response to varying amplitudes ofinput voltage.

It is another object to accomplish distortion compensation over arelatively extensive range of amplitudes of the input voltage.

It is a still further object to control the production of modulationproducts in carrier transmission systems.

It is still another object to provide different orders of modulation ina. carrier transmission system embodying a common source of carrierwaves.

As pointed out in the copending application of E. Peterson, supra,composite waves entering one or more repeaters in tandem in atransmission system will cause to occur in the output of each repeater,certain modulation products which will tend to accumulate from repeaterto repeater. A non-linear modulating apparatus comprising preferably aplurality of non-linear resistance elements arranged in a bridge networkand having one diagonal applied to the line at the output of apreselected repeater serves to eiiect neutralby introducing into theline at the output of the preselected repeater certain modulationproducts in phase opposition to the repeater produced modulationproducts.

In a preferred embodiment, this invention relates to a variably negativeself-biasing arrange= ment applied to the other diagonal of thenonlinear bridge networlz and comprising in series a resistor having afixed resistance characteristic and a resistor having a non-linearresistance characteristic, and a capacitor applied in shunt of bothlatter resistors.

A feature of the invention is that the amplitude of the signalingvoltage controls the variably neg ative self-biasing voltage so that acertain law of variation of the modulation products produced by thenon-linear. bridge network may be obtained over a range of amplitudes ofsignaling voltage. Such feature has a particular application in thedistortion neutralization arrangement mentioned in the copendingapplication of E. Peterson, supra. Another feature is that thenon-linear bridge network may be expeditiously adapted to provide incarrier transmission sys-- tems certain orders of modulation. In thelatter connection two or more non-linear bridges may be utilized with acommon source of carrier waves to eflect modulation products ofdifferent orders of modulation, each non-linear bridge bieingoperatively associated with a suitably selective filter to transmit acertain order of modulated component to each discrete signaling channel.

The invention will be readily understood from I the followingdescription taken together with ization oi the accumulated modulationproducts invention in a system to combine signaling and carrier waves incertain desired components for selection by a load and in which thesignaling and carrier sources and the load are connected in series;

Fig. 6 is a modification of Fig. in which the signaling source and loadare connected in series and the carrier source is applied in shunt ofboth thereof; and

Fig. 7 is a schematic diagram embodying an 5 expansion of Fig. 6 toeffect modulation products of different orders of modulation by using acommon source of carrier'waves.

The same reference numerals are utilized to designate identical elementsappearing in the 0 several figures of the drawing.

Fig. 1 embodies curves having current and voltage plotted as therespective ordinate and abscissa of non-linear apparatus producing third-ordermodulation products. Curve A is a plot of side of the line in theoutput of the repeater I2 is an impedance it which possesses such valueof resistanceas to cause relatively small line unbalance. Connectedacross the impedance [4 is an attenuator i5 which is applied to onediagonal of a non-linear bridge network it comprising a plurality ofnon-linear resistance elements i'l. Therepeaters ii and i2 are eachpreferably a vacuum tube amplifier having either an expanding orcompressing characteristic regarding the production of third ordermodulation products. As seen in Fig. 2, the non-linear network iseffectively connected in series in the line and may possess either anexpanding or compressing characteristic concerning the production ofthird order modulation products.

Assuming a composite wave of frequency com- 40 ponents p and q impressedon the input of the line, then it may also be assumed that among otherproducts the output of the repeater i2 contains the products 2?, q, and2pq. These products will cause individual potential drops across theimpedance it at the respective frequencies. Accordingly, current of thefrequencies p, q and 2H will be caused to flow in the bridge network.From this it may be assumed that the output of the bridge network willchiefly include current of the components p, q, Zp-q. The third orderproduct 2p-q in the output of the bridge network is approximately 180degrees out of phase with the third order product 2p-q in the output ofthe repeater ii, if the repeater l2 effects a compressing characteristicand the bridge network effects an expanding characteristic, or viceversa. Con sequently, these discrete third order products willsubstantially neutralize each other, as the magnitude of output of thebridge network may be controlled by the attenuator l5. While theneutralization of only one specific third order modulation product ismentioned, it is to be understood that such neutralization may beaccomplished by the single network IS with regard to all third ordermodulation products. The prdoucts to be, neutralized may be due torepeater I 2, alone, or the accumulated products due to repeaters H andI 2.

Fig. 3 shows a section of a signaling transmission line in which thenon-linear network is effectively applied in shunt of the line; In thisconnection it is understood that the portion of Fig. 2 above the lineX-X is to be included above 75 the line X-X of Fig. 3, and therefore theoperation of Fig. 3 is substantially the same as that pointed out abovefor Fig. 2. Thus, the third order products efiected by one or morerepeaters are substantially neutralized by introducing into the outputof the latter in phase opposition equivalent modulation productsgenerated by the non-linear network.

A more complete description of the aforedescribed action may be had byreferring to the copending application of E. Peterson, supra.

In accordance with this invention, the amplitudes of the modulationproducts eflected by the non-linear bridge network are controlled so asto be substantially identical with the amplitudes of the modulationproducts generated by the line repeaters over a. range of amplitudes ofinput voltage in order to obtain substantially complete neutralization.In other words, such neutralization is efiiciently accomplished whenboth the line repeaters and the non-linear bridge network followsubstantially the same law of variation over the same range ofamplitudes of input voltages. Such variation is assumed to be a cube lawfor the purpose of this illustration.

Consequently, this invention provides that the third order modulationproducts effected by the non-linear bridge network vary as the cube ofthe input voltages over a relatively large range of amplitudes of thelatter. This law of variation is obtained by applying a variablenegative self-bias to the discrete non-linear resistance elements of thebridge network in a manner that will be presently explained. Referringto Fig. 2, the diagonal of the bridge network opposite to that appliedto the line embodies in series an element til having a fixed resistancecharacteristic and an element til having a non-linear resistancecharacteristic, and in shunt of both latter elements a capacitor t2.

An alternate embodiment of the invention shown in Fig. 4 comprises theresistors Ml and ll and capacitor 42 applied in parallel to the oppositediagonal of the bridge network. In this connection it is to beunderstood that the circuit portion above the line XX of Fig. 4 may besubstituted for the circuit portion above the line X--X of Figs. 2 and3.

The law of variation of the third order modulation products effectedby'the non-linear bridge network may be changed by adjusting the valueof the fixed resistance 40 and the value of the non-linear resistanceelement 4!. The function of the capacitor $2 is to short-circuit anyalternating current so that the network comprising resistance elements30 and 41 and the capacitor :32 responds only to direct current andtherefore acts as a direct-current resistance. In this connection it is,of course, understood that thedirect current is obtained by'rectification of the signaling voltage. Thus, the network comprising theresistors 40 and 4| and capacitor 42 serves to apply a variable negativeself-bias to the discrete non-linear elements in response to varyingamplitudes of input voltage. An outstanding feature of this arrangementis that the use of the non-linear element 4| provides that the cube lawof variation is effective over a relatively large range of amplitudesof'input voltage.

While the above has been described with regard to the neutralization ofrepeater-produced distortion, it is to be understood that similarneutralization could be eifected for distortion caused by othercomponents of a signaling system.

The invention is also applicable to modulating and demodulating systemsto produce desired orders of modulation. Referring to Fig. a signalsource 50, a carrier source 5! and a load 52 are applied serially to.the vertical diagonal of the non-linear bridge network I6. Anoutputfilter 53 interposed between the vertical diagonal of the bridgenetwork I. and the load 52 serves to select the desired modulatedcomponent. Referring to Fig. 6, the signal source'and load are connectedserially to the vertical diagonal of the bridge network while thecarrier source is applied to the horizontal diagonal thereof. Theself-biasing network comprising resistors 40 and 4| in series andcapacitor 42 in shunt of both thereof as shown in Fig. 2 is applieddirectly to the horizontal diagonal of the non-linear bridge network ISin Fig. 5, and to the same diagonal in series with the carrier source 5|in Fig. 6. In this connection it is to .be understood that theself-biasing network may also comprise the resistors 4|! and 4| andcapacitor 42 in parallel as shown in Fig. 4 and this may also beemployed in Figs. 5 and 6. In Figs. 5 and 6 the signal and carrier wavesare combined in the well-known manner to produce a signalv modulatedcarrier wave. For a more complete understanding of such action,reference is made to the patents of F. A. Cowan and R. S. Caruthers,Nos. 1,959,459 and 2,086,601, grantedMay 22, 1934, and July 13, 1937,respectively.

As previously pointed out in connection with this invention as shown inFigs. 2, 3 and 4 the law of variation of the modulation productseffected by the non-linear bridge network may be changed by adjustingthe value of the fixed resistance 40 and the value of the non-linearresistance l I, and thereby the value of the negative self-bias appliedto the individual non-linear elements constituting the bridge network.Accordingly, the law of variation of the non-linear network to eflect adesired modulated product for selection by the band filter 53, Figs. 5and 6, is rendered effective by such negative self-bias over arelatively large range of signal-voltage amplitudes. The modulationaccomplished by the arrangements of Figs. 5 and 6 is preferablydescribed as third order, although second or other order may also beexpeditiously achieved.

The invention is further applicable to produce different orders ofmodulation in the same carrier system. Referring to Fig. '7, which is anexpansion of Fig. 6, a signal source Q1 and load L1 are applied inseries to the vertical diagonal of a bridge network 60, and a signalsource Q2 and load 1a are applied in series to the vertical diagonal ofa bridge network 6|. Across the horizontal diagonals of both bridgenetworks 60 and 6| is a common carrier wave source P. The self-biasingarrangement comprising the series resistors 40 and 41 shunting capacitor42 as shown in Fig. 2 is applied to the horizontal diagonals of each ofthe bridge networks 66 and 6| in series effectively with the carriersource P, and is identical with the correspondingselfbiasing arrangementapplied to the horizontal diagonal of the bridge network I6 illustratedin Fig. 6. In this connection it is to be understood that theself-biasing arrangement comprising the resistors 40 and 4| andcapacitor 42 in parallel 'may also be employed in Fig. 7.

In the operation of Fig. 7, the bridge network 66 is self-biased toproduce second order modulation and the band-pass filter 62 is designedto select either the upper or lower side-band of the products PiQi,depending on the modulated component to be transmitted to the load L1;and

the bridge network 6| is self-biased to effect third order modulationand the band-pass filter 63 is designed to select either the upper orlower sideband of the products 2PiQ2, depending on the modulatedcomponent to be transmitted to the load L2. It is to be understood thatother orders of modulation may be accomplished by connecting additionalsignaling systems across the common carrier source P in the manner ofthe sys tems embodying signal source Q1 and load L1 and signal source Q2and load In, respectively. A more complete understanding of themodulation action may be had by referring to the Cowan and Carutherspatents, supra.

A feature of the invention as applied to Figs.

5, 6 and '7 is that the amplitude of the signaling voltage'so controlsthe variably negative selfbiasing voltage that a certain law ofvariation of the modulation products effected by the nonlinear bridgesmay be obtained over a range of amplitudes of signaling voltage. Inother words, the desired modulated component may be obtained regardlessof large variations of the amplitude of the signaling voltage.

What is claimed is:

1. In combination, a plurality of non-linear resistance elementsarranged in the form of a bridge for effecting modulation products,means to aptain modulation products possess amplitudes controlled by arange of amplitudes of the complex waves.

2. In the combination according to claim 1 in which the impedancenetwork comprises reactive and resistive elements, the resistiveelements being of fixed and non-linear resistance characteristics.

3. In the combination according to claim 1 in which the impedancenetwork comprises in series a resistive element having a fixedresistance characteristic and a resistive element having a nonlinearresistance characteristic, and in shunt of both latter elements acapacitive element.

4. In the combination according to claim 1 in which the impedancenetwork comprises in parallel a capacitor and two resistors, both latterbeing of fixed and non-linear resistance characteristics.

5. In combination, a transmission line for alternating current signalingwaves, means embodied in said line for translating signaling waves intounwanted modulation products, and means for neutralizing said unwantedmodulation products by introducing equivalent modulation products in theoutput of said first-mentioned means in phase opposition to saidunwanted modulation products, said second-mentioned means comprising aplurality of non-linear resistance elements having a bridgeconfiguration of which one diagonal is connected to said line in theoutput of said first-mentioned means to translate signaling waves insaid line into neutralizing modulation products equivalent to saidunwanted modulation products, and impedance means having a non-linearresistance characteristic and applied to the opposite diagonal of saidbridge to bias said elements thereof with an effective negative directpotential, due to rectification of said signaling waves by said bridge,such that the amplitudes of said equivalent neutralizing modulationproducts are substantially equal to the amplitudes of said unwantedmodulation products over a range of amplitudes of said signaling waves,said impedance biasing means comprising reactive and resistive elements,the resistive elements having fixed and non-linear characteristics.

6. In combination, a transmission line for alternating current signalingwaves, a plurality of discrete means embodied in said line and subjectindividually to the production of unwanted :modulation products tendingto accumulate from one discrete means to the others in response tosignaling waves in said line, means comprising a plurality of non-linearresistance elements arranged in a bridge configuration to generate, inresponse to signaling waves in said line, neutralizing modulationproducts equivalent substantially to said unwanted modulation products,circuit means to apply one diagonal of said bridge to the output of oneofsaid discrete means to interpose in the output of said one discretemeans said equivalent neutralizing modulation products in phaseopposition to said unwanted modulation products thereby neutralizingsaid latter products, and impedanc means having a non-linearcharacteristic and applied to the other diagonal of said bridge to biassaid elements thereof with an effective negative direct potential, dueto rectification of said signaling waves by said bridge, such that theamplitudes of said equivalent neutralizing modulation products aresubstantially equal to the amplitudes of said unwanted modulationproducts over a range of amplitudes of said signaling waves, saidimpedance biasing means comprising a capacitor andresistors having fixedand non-linear resistance characteristics.

7. In combination, atransmission line for alternating current signalingwaves, apparatus embodied in said line and producing unwanted modulationproducts in response to signaling waves in said line, and means forneutralizing said unwanted modulation products by introducing equivalentmodulation products in the output of said apparatus in phase oppositionto said unwanted modulation Droducts, said means comprising a pluralityof non-linear resistance elements arranged in the form of a bridge whoseone diagonal is connected to said line in the output of said apparatusto produce, in response to signaling waves in said line, neutralizingmodulation products equivalent substantially to said unwanted modulationproducts, and meansto bias said elements of said bridge with aneffective negative direct potential, due to rectification of saidsignaling waves by said bridge, such that the amplitudes of saidequivalent neutralizing modulation products are substantially equal tothe amplitudes of corresponding unwanted modulation products over arange of amplitudes of said signaling waves, said biasing meanscomprising a resistor having a fixed resistance characteristic and aresistor having a non-linear resistance characteristic, both of saidresistors being applied in series to the other diagonal of said bridge,and a capacitor applied in shunt of both said resistors.

8. In combination, a transmission line for alternating current signalingwaves, at least one repeater embodied in said line and subject to theproduction of unwanted modulation products in response to signalingwaves therein, a plurality of non-linear resistance elements arranged ina bridge configuration to generate, in response to signaling waves'insaid line, neutralizing modulation products equivalent substantially tosaid unwanted modulation products, circuit means to apply one diagonalof said bridge to the output of said repeater to interpose therein saidequivalent neutralizing modulation products in phase opposition to saidunwanted modulation products thereby neutralizing said latter products,and impedance means having a non-linear characteristic and applied tothe other diagonal of said bridge to bias said elements thereof with aneffective negative direct potential, due to rectification of saidsignaling waves by said bridge, such that the amplitudes of saidequivalent neutralizing modulation products are substantially equal tothe amplitudes of said unwanted modulation products over a range ofamplitudes .of said signaling waves, said impedance biasing meanscomprising in series a resistor having a fixed resistance characteristicand a resistor having anon-linear resistance characteristic, and inshunt of both said resistors a capacitor.

9. In combination, a transmission line for altemating current signalingwaves, a plurality of repeaters embodied in said line and subjectindividually, in response to signaling waves in said line, to theproduction of unwanted modulation products tending to accumulate fromrepeaterstantially to said accumulated unwanted modulation products,circuit means to apply one diagonal of said bridge to the output of oneof said repeaters to interpose in the output of said one repeater saidequivalent neutralizing modulation products in phase opposition to saidaccumulated unwanted modulation products thereby neutralizing saidunwanted modulation products in the output of said one repeater, andimpedance means having a non-linear resistance characteristic andapplied to the other diagonal of said bridge to bias said elementsthereofwith an efl'ective negative direct potential, due torectification of said signaling waves by said bridge, such that theamplitudes of said equivalent neutralizing modulation products aresubstantially equal to the amplitudes of corresponding unwantedmodulation products over a range of amplitudes of said signaling waves,said impedance biasing means comprising in series a resistor having afixed resistance characteristic and a resistor having a non-linearresistance characteristic, and in shunt of both said resistors acapacitor.

10. In combination, a transmission line for alternating currentsignaling waves, apparatus embodied in said line and producing unwantedmodulation products in response to signaling waves in said line, andmeans for neutralizing said unwanted modulation products byintroducinglequivalent modulation products in the I output of saidapparatus in phase opposition to said unwanted modulation products, saidmeans comprising a plurality of non-linear resistance elementsarrangedin the form of a bridge whose one diagonal is connected to saidline in the output of said apparatus to produce, in response tosignaling waves in said line, neutralizing modulation productsequivalent to said unwanted modulation products, and impedance meanshaving a non-linear characteristic and applied to the other diagonal ofsaid bridge to bias said elements thereof with an efiective negativedirect potential, due to rectification of signaling waves by saidbridge, such that the amplitudes over a range of amplitudes of saidsignaling waves, said impedance biasing means comprising in parallel aresistor having a fixed resistance characteristic, a resistor having anon-linear resistance characteristic, and a capacitor.

11. In combination, a, transmission line for alternating currentsignaling. waves, a plurality of repeaters embodied in said line andsubject individually, in response to signaling waves in said line, tothe production of unwanted modulation products tending to accumulatefrom repeater torepeater, means comprising a plurality of non- Lnearresistance elements arranged in a bridge configuration to generate, inresponse to signalin; waves in said line, neutralizing modulationproducts equivalent substantially to said un-' wanted modulationproducts, circuit means'to apply one diagonal of said bridge to theoutput of one of said repeaters to interpose in the output of said onerepeater said equivalent neutralizing modulation products in phaseopposition to said accumulated unwanted modulation products therebyneutralizing said unwanted modulation products in the output of said onerepeater, and

impedance means having a non-linear resistance characteristic andapplied to the other diagonal of said bridge to bias said elementsthereof with an efiective negative direct potential, due torectiflcation of said signaling waves by said bridge, such that theamplitudes of said equivalent neutralizing modulation products aresubstantially equal to the amplitudes of corresponding accumulated'unwanted-modulation products over a range oi. amplitudes of signalingwaves, said biasing means comprising in parallel a resistor having' afixed resistance characteristic, a resistor having a non-linearresistance characteristic, and acapacitor.

- PAUL A. REILING.

